A misunderstanding about lime and gypsum is that if you mix them or apply them together they will be antagonistic or “fight” one another. Another misunderstanding is that gypsum is for high pH soils and lime is for low pH soils. In actuality, gypsum can be applied and has benefits in both high pH soil and low pH soils. Gypsum and lime applied together can actually have synergistic effects.
So why would we want to apply gypsum and lime together? I will outline several reasons. First lime is insoluble in water so it is relatively immobile in the soil. Contrast that with gypsum which is water soluble and has much greater mobility in the soil. Gypsum therefore improves soil conditions much more rapidly than lime and will affect soil conditions to a greater depth than lime will. Gypsum will supply calcium to deeper depths than lime. This will improve subsoil conditions, and allow for greater root growth (better nutrient and water efficiency). If aluminum toxicity is an issue due to acid subsoils, the gypsum will also react with the aluminum to offset its effect. As a result, root depth will be greater and nutrient availability will be improved.
Lime can initially cause a cementing of the soil at the surface decreasing water infiltration. By applying gypsum with the lime you will negate this surface sealing affect. With improving soil conditions, lime movement will be greater.
Lime will have a much more pronounced effect on soil pH than gypsum will, however, the pH change will be near the surface where the lime is placed.
Lime is often times dusty and can become air borne when applied. The most reactive lime is the dust so you will not realize the benefits of this lime if it lands on your neighbor’s field. By applying gypsum with the lime you can apply a very high quality lime source and control the dustiness of the lime. The application will be dust free.
If you have variable soils and areas with high pH you won’t want to apply lime in those areas, but still may want to apply gypsum. In those situations, a mix of lime and gypsum may not be ideal.
Applying lime/gypsum mixes are becoming more common by our customers. A 50:50 lime/gypsum mix is most often used in our area. Typically, the rates of each product are 1000 or 2000 pounds per acre.